Publishing Free/Busy Data

Topic Last Modified: 2006-03-13

The process of publishing free/busy data from the user's client application to the appropriate free/busy folder depends in part on the client that the user has. Outlook and other MAPI-based clients function somewhat differently in this respect from Web-based clients such as Microsoft Office Outlook Web Access for Exchange Server 2003 and Microsoft Outlook Mobile Access.

By default, Outlook publishes the free/busy data for a user one time every 15 minutes, and again when Outlook shuts down. When publishing, Outlook updates the entire free/busy message instead of just adding changes to the existing message. The message includes free/busy data that ranges from the current month to two months in the future.

Outlook users can customize the free/busy settings, including the following:

Publishing interval, which can be as short as one minute.

Number of months in the future to publish, which can be as long as 36 months.

The following figure provides an overview of how Outlook publishes a user's free/busy data.

Tasks involved when Outlook publishes free/busy data

When Outlook has to publish, it first identifies the appropriate free/busy subfolder. Outlook retrieves the legacyExchangeDN attribute from the user's account in the Active Directory directory service. Then, Outlook divides the legacyExchangeDN value. It uses the first part to identify the user's administrative group and therefore the appropriate free/busy subfolder. It uses the second part as the subject of the free/busy message.

Note:

The legacyExchangeDN value always refers to the administrative group where the user's mailbox was originally created.

For example, consider a user with the legacyExchangeDN of /o=Microsoft/ou=APPS-ABC/cn= RECIPIENTS/cn=ASAMPLE. The user's free/busy data is stored in a message with the subject line USER-/cn=RECIPIENTS/cn=ASAMPLE. The message is posted in the folder EX:/o=Microsoft/ou=APPS-ABC, which is a subfolder of SCHEDULE+ FREE BUSY.

Note:

Some errors or replication issues may produce duplicate free/busy messages for a single user. These messages have -2 appended to the subject line (for example, USER-/cn=RECIPIENTS/cn=ASAMPLE-2).

After identifying the free/busy folder, Outlook selects a public folder server where it can post the message. Outlook has to find a public folder server that has replicas of the appropriate subfolders of the SCHEDULE+ FREE BUSY system folder.

The process that Outlook uses to locate a free/busy folder is similar to the normal public referral process that Exchange Server 2003 uses for Outlook. Outlook uses the following steps to locate a free/busy folder:

Outlook contacts the user's mailbox store to determine the location of the associated (default) public folder store, which can be on the same server as the mailbox store or on a different dedicated public folder server.

Outlook tries to publish free/busy data to the user's default public folder store.

If the default public folder store is unavailable, Exchange Server 2003 sends Outlook to another public folder store that supports the default Public Folders tree.

If this new public folder store does not contain replicas of the free/busy folders (which is likely to be the case), Exchange Server 2003 returns a list of servers that do contain replicas, prioritized by an internal algorithm. If the referring server has a configured list of referral servers, Exchange Server 2003 uses that list.

Note:

If multiple servers meet the criteria for a referral, Exchange Server 2003 uses a hashing algorithm to select one preferred server for the user. Using this algorithm, Exchange Server 2003 can load balance users among the public folder stores while consistently sending a specific user to a specified store.

Outlook tries to publish the data to the first public folder server in the list. It continues down the list until it succeeds.

As a result of this referral process, there is no guarantee that the free/busy information will always be published to the same public folder store. However, the information will eventually be replicated to all stores. This referral process is automatic and cannot be disabled.

Outlook Web Access and Outlook Mobile Access do not publish free/busy data directly to the public folder store. Instead, they rely on a free/busy publishing agent that is named MadFB (also known as MSExchangeFBPublish), which runs as part of the Microsoft Exchange System Attendant service (MSExchangeSA). MadFB has two functions. It publishes free/busy messages for Outlook Web Access and Outlook Mobile Access, and it deletes duplicate free/busy messages. In this section, the first function is discussed.

Note:

Microsoft Entourage for the Macintosh also relies on this MadFB process to publish free/busy data.

Instead of publishing at preset intervals, Outlook Web Access and Outlook Mobile Access publish free/busy data when a user saves a new appointment, deletes an appointment, or saves changes to an appointment's start time or end time. The following figure shows the basic steps of the publishing process.

Publishing free/busy data with a Web-based client using a front-end/back-end Exchange topology

When Exchange Server 2003 commits the change, it sends a free/busy message to the system attendant mailbox.

Polling at intervals (the default is 5 minutes), MadFB retrieves the free/busy message and publishes it to the free/busy public folder.

MadFB uses the same process for publishing free/busy data that Outlook uses. As with Outlook, Exchange Server 2003 refers MadFB to an appropriate public folder store. Any duplicate free/busy messages have -2 appended to the message subject.

Note:

Because most of the processing is handled by the Exchange servers instead of the client, using Outlook Web Access and Outlook Mobile Access can provide performance and reliability advantages over Outlook.